During the incubation period (remember, don't disturb the eggs in any way until they're eyed up) some eggs will turn white which indicates that they are dead. When the eggs are eyed up it is normal to submit them to a mild bump that will cause the infertile eggs to turn white. At this point, all of the white eggs should be removed. If you put a white egg in a strong vinegar solution the egg will turn transparent and it will be easy to see what stage of development the embryo was in when it turned white. If no embryo is present, or only a white spot shows, it usually means that the egg was not fertilized or that it was injured in some way at the very beginning stage of incubation. The actual taking and fertilizing of the spawn is the same for both domestic and wild fish. Many fishery operations are taking rainbow trout during the fall and winter. The Rainbow is naturally a spring spawning fish but when held in constant water temperatures of around 50 degrees F, the Rainbow will gradually change to a fall and winter spawner. These fish can be further manipulated with the use of enclosed sheds with artificial lighting over the raceways or structures where the fish are being held. The enclosure must be totally dark with the only light coming from electric light bulbs. A timer is used to produce the desired amount of light for the length of time needed to further regulate the spawning.